The hippocampus participates in the regulation of emotions and contains small amounts of met5-enkephalin but a relatively high amount of receptors. The met-enkephalin content differs in various regions of the hippocampus. The temporal region contains three times more met-enkephalin than the septal region. The CA3 and CA4 regions contain twice the met-enkephalin content of CA1, CA2, and subiculum. The uneven distribution of met-enkephalin within the hippocampus suggests that met-enkephalin neurons may be located in specific sites where they regulate pyramidal cell activity. Studies using both mechanical and chemical lesions suggest that ME containing neurons are short axon interneurons within the hippocampus. The hippocampus ME content increases after the animals exhibit recurrent motor seizures. This result suggests that the met-enkephalin neurons may respond to certain pathological conditions and may be associated with the postictal depression.